Digital watermarking is a process for modifying physical or electronic media content to embed a hidden machine-readable code into the media. In digital watermarking, a media content signal, such as an image or audio signal, is modified to embed a hidden, digital auxiliary code signal such that the auxiliary signal is imperceptible or nearly imperceptible to the user, yet may be detected through an automated detection process. Most commonly, digital watermarking is applied to media content signals such as images, audio signals, and video signals. However, watermarking may also be applied to other types of media objects, including documents (e.g., through line, word or character shifting, through background patterns or tints, etc.), software, multi-dimensional graphics models, and surface textures of objects.
Digital watermarking systems typically have two primary components: an encoder that embeds the watermark in a host media signal, and a decoder that detects and reads the embedded watermark from a signal suspected of containing a watermark (a suspect signal). The encoder embeds a watermark by subtly altering the host media signal. The reading component analyzes a suspect signal to detect whether a watermark is present. In applications where the watermark encodes information, the reader extracts this information from the detected watermark.
Several particular watermarking techniques have been developed. The reader is presumed to be familiar with the literature in this field. Particular techniques for embedding and detecting imperceptible watermarks in media signals are detailed, e.g., in the assignee's co-pending U.S. patent application Ser. No. 09/503,881 (U.S. Pat. Nos. 6,614,914) and 6,122,403, which are each hereby incorporated by reference.
Another technology referred to as fingerprinting, in contrast to digital watermarking, does not embed auxiliary data in a media signal, but rather, derives a unique content signal identifier from the media signal itself. For some applications where the signal undergoes a transformation in normal use, such as compression, transmission, or digital to analog to digital conversion, the fingerprint (or host signal characteristics used to determined a fingerprint) preferably remains relatively unchanged, allowing unique identification of the content signal. Fingerprints for a wide selection of media signals may be stored in a database and associated with information or actions to be taken upon detection or calculation of a fingerprint.
Aspects of the present invention are now discussed relative to three related environments; namely, i) Copy Once Systems; ii) PC Buffer Copy Protection; and Efficient Interaction of Several Watermarking Systems for Copy Control. (Of course, my inventive techniques can be applied to many other environments as well.).
Copy Once Systems
In some applications, it is critical to copy protect digital content, such as DVD videos, since it is easy and fast to make exact digital reproductions. Digital watermarking, data headers, and encryption systems can be used to designate content as a particular copy state, such as: copy never, copy once, copy no more, or copy freely (where copy freely is sometimes signaled, e.g., by the lack of a digital watermark, header, or encryption system).
On pre-recorded read-only media (e.g., media including a digital watermark indicating “copy once” content), a copy of the read-only media (or “duplicate copy”) is turned into “copy no more” by adding a robust watermark or removing a fragile watermark. This digital watermark (or removal of a fragile watermark) indicates that the duplicate copy is indeed a copy (which is perhaps designated as a “copy never” state). However, the original “copy once” read-only content can be copied again and again on the same recording device.
Similarly, on pre-recorded read-only media, a file header and/or encryption system can also only enable copy one generation because the original media cannot be modified (as it is read-only). The duplicate copy of the recorded media can be updated as copy no more by changing the header or encryption system metadata, but not the original. As such, the original can be copied again and again on the same device.
To stop a device from creating multiple copies of “copy once” content, a digital watermark, fingerprint, or out of band header identifier (ID) can be used to identify content (referred to as a “content ID” or “content identifier”) and a content ID can be stored in a recorder device (e.g., in a case where content is labeled or designated as copy once). When content is to be recorded, its content ID is checked, and if it matches or coincides with a stored content ID on that device or within a personal home network (PHN), recording is not enabled, prevented or stopped. (I also envision a scenario where a content ID is stored remotely from a copy device (e.g., accessible via the internet or home network), and a copy or recording device queries the remote database to determine whether to allow copying.). This process turns a copy one generation into copy once for this device or PHN. The user can copy the original in another recorder or PHN, but only once, and this becomes expensive to have one device or PHN for every copy—as well as helps devices or PHNs identify a pirate as opposed to a consumer wanting an archival copy.
PC Buffer Copy Protection
Currently, no matter if there is hardware encryption protection, such as Microsoft (MS) Palladium (now called Next-Generation Secure Computing Base (NGSCP)), or software encryption protection, such as MS SAP (secure audio path) or IBM EMMS (electronic media management system), a consumer can easily bypass the security by recording the decrypted output buffer after rendering. For example, on many IBM Thinkpads (such as the year 2000 600× model) the soundcard can digitally record the output play buffer by setting the recording option in Windows mixer to loopback. Thus, a perfect copy of any protected music can be made.
Currently, there are products to digitally capture the sound buffer, even when loopback options are not available in the mixer, such as with Total Recorder from High Criteria, Inc. Similar products will be made for video capture, but are not available yet because, e.g., people are just starting to watch valuable video on the PC.
In addition, anyone can easily copy audio and video by physically looping back the final, usually analog, output. For example, a person can record audio on the PC by connecting the audio line out (e.g., an output port) to the audio line in (e.g., an input port) with an inexpensive (only several dollars) cable with two ⅛″ stereo plugs, as sold at Radio Shack, for connecting speakers to a sound card. Similarly, a person can record the video on a PC by connecting the S-video out to the video in on a PC equipped with a video output and capture card, or via a digital camcorder connected to a PC. Soon, PCs will have digital audio and video outs, which can be physically looped back for perfect copying.
This type of recording can be stopped on a PC or a group of networked PCs by comparing a content ID of content stored in the input buffer with a content ID of content stored in the output buffer of the PC or a group of networked PCs and stopping or preventing recording if the content IDs match (e.g., assuming the content is protected content). This system significantly raises the barrier of copying by requiring the consumer to use 2 non-networked PCs.
Efficient Interaction of Several Watermarking Systems for Copy Control
Many watermark-based copy control systems are designed for one digital watermark protocol and one system. For example, one video watermark can provide play and record control for DVDs. Another video watermark, probably related to but slightly different than for DVD, for example, can provide similar functionality for another system, such as conditional access (hereafter “CA”) television (TV).
The copy control watermark can provide four copy control states, including copy never, copy once, copy no more, and copy freely. In one implementation, bits of a digital watermark payload, e.g., where 2 bits are needed for each state, provides this functionality. In an alterative implementation, a digital watermark embedded according to a different key indicates which copy control state is associated with the media content.
For example, four different keys, each representing a different copy control state, can be used. The key is preferably a pseudo-random sequence that is used to embed the watermark, but it need not be. For example, the key can specify locations for watermark embedding, host signal features to be modified to effect embedding, indicate a watermark characteristic, and/or semantic meaning of particular features (e.g., how modifications to the host signal are mapped to particular data symbols, such as binary or M-ary symbols), etc.
There can be additional states like pause, length of pause, analog output enabled, secure digital output required, etc.
However, an overall system, to efficiently provide a similar, but different, copy control watermark, has not been defined.
My solution can provides different copy protection systems or phases of a system by varying a watermark key or keys, and/or by embedding additional bits into the digital watermark payload.
Further features and advantages of the invention will become even more apparent with reference to the following detailed description and the accompanying drawings.